Carnegie Stage 1

Introduction

Stage 1 is the unicellular embryo that contains unique genetic material and is an individually specific cell that has the potential to develop into all of the subsequent stages of a human being. It is the beginning of embryonic life and ontogenetic development that starts when an oocyte, arrested in metaphase of meiosis II, is penetrated by a sperm. This is the first event of fertilization. The embryo has a postfertilization age of approximately one day, is between 0.1 to 0.15 mm in diameter and weighs approximately 0.004 mg.